Whole-body and regional basal lipolytic rates, the lipolytic response to exercise, and lipolytic sensitivity to epinephrine infusion will be determined in obese and lean subjects by infusing (2H5) glycerol and (1-13C) palmitate in conjunction with abdominal vein catherterization and microdialysis probe insertion. Adipose tissue biopsies will be obtained to assess the molecular mechanisms regulating regional lipolysis.